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Prof. Keeble, Dr. Armstrong, and Mr. Jones. [Feb. 3, 



Yet more conclusive is the result when the blue solution, produced by 

 the action of bran peroxydase and hydrogen peroxide on benzidine, is added 

 to the residue obtained by evaporating alcohol which has been in contact 

 with intact petals. The blue colour of the former is discharged immediately, 

 that is to say, the action of the oxydase is reversed, and the blue product 

 of the oxidation of benzidine is reduced to its original colourless state. That 

 this effect is not due to reducing agents present in the alcohol is shown by 

 the fact that no discharge of colour is brought about by the addition of the 

 blue oxydase-benzidine solution to the residue left after the evaporation of 

 alcohol which has not been in contact with petals. This method of 

 demonstrating the presence of a reducing agent is the more conclusive in 

 that whereas alcohol alone reduces oxydase-activity, it does not bring about 

 a reversal of the action. The only effect of alcohol on the blue colour is to 

 precipitate the blue pigment. 



We have shown in a previous communication (Part III) that the oxydases 

 of the flower not only act on the forerunners of pigment contained in the 

 petals but also on the artificial chromogen benzidine and give rise to pigments ; 

 we now show that flowers contain reducing agents which are not only capable 

 of inhibiting the action of oxydase, but are able also to reduce both the 

 natural pigments of the flower and the " artificial " benzidine pigments to the 

 colourless state of chromogens. 



Two facts stand out prominently in the foregoing investigation of 

 decolorisation. These facts are that the reducing agent is very resistant to 

 high temperatures and that it is active in strong alcohol. The former we have 

 studied in sufficient detail only to be able to state that the reducing agent is 

 not destroyed by exposure to a temperature of 100° C, the latter fact has 

 been investigated more fully and with the following, results : — 



Both evolution of gas and fading of the flower take place rapidly in alcohol 

 of 95 per cent. These processes go on, albeit more slowly, in yet stronger 

 alcohol. Thus with the ordinary absolute alcohol of the laboratory (99 per 

 cent.) a certain amount of gas is evolved and colour begins to disappear ; but 

 when petals are placed in alcohol of approximately 100 per cent, both 

 processes, although they take place, come to an end much sooner than in the 

 alcohol of slightly lower grade. 



We conclude, therefore, that the reducing agent which brings about 

 decolorisation of the petals of stocks is able to exhibit its specific action in 

 tissues which are almost completely dehydrated. We have, moreover, 

 evidence that loss of colour occurs naturally in the plant. We know, for 

 example, that in many plants light shades of colour are dominant to dark 

 shades ; we know also that the flowers of such plant of stocks may assume as 



